The present invention relates to magnetic resonance imaging and, in particular, to local coils for use in magnetic resonance imaging.
Magnetic resonance imaging (MRI) detects the faint nuclear magnetic resonance (NMR) signals given off by protons in the presence of a strong magnetic field after excitation of the protons with a radio frequency signal. The NMR signals are detected using loop antennas termed “coils”.
NMR signals are extremely faint and therefore “local coil” or “surface coils” may be designed such as can be placed in close proximity to the region of interest of the imaged object. The size of the local coils is kept small to allow them to be easily fit to the patient on the MRI patient table. Importantly, the small area of loops of the local coil provides improved signal strength relative to received noise. The local coils are in contrast to the whole body coil typically present in an MRI machine and useful for obtaining broad “survey” scans of the patient.
The small size of a local coil generally limits the volume over which the coil is sensitive. For imaging large areas of the body, for example, neurovascular imaging of the head, neck, and lower spine, the whole body coil with its lower signal to noise ratio must be used. Alternatively, coverage of this region can be obtained by using several local coils and taking multiple images of the patient and changing or repositioning the local coil in between images. This latter approach is time consuming and impractical in many situations.